Ditto about starting with great piece of meat. If you don't, no kitchen wizardry will make up the difference.
Well marbled steak is best in general. Prime bone-in ribeye is personal fave, as the bones help keep the steak juicy. (Bones have similar effects in chicken and fish, actually.)
Some good steakhouses, like Ruths Chris, will warm up butter until it becomes liquid, then drop steak in it for 20 minutes prior to cooking. Adds to sear and to flavor.
Also, dry-aged beef has more concentrated flavor.
Personally I love teriyaki marinated flank steak, but that is more of a specialty item. Flank steak is pretty darn lean, even the best, so anything beyond medium rare is not recommended.
